Two strings of equal length are stretched out with equal tension. the second string is four times as massive as the first string. if a wave travels down the first string with velocity v , how fast does a wave travel down the second string?

C. it comes from the core of the earth.

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.